A standard waterproof box is mainly formed of a polyethylene-coated cardboard sheet that is given to start with four parallel longitudinal creases subdividing it into four adjacent relatively wide side panels and one fairly narrow end seal flap. A so-called tube blank is first made by holding the blank flat heating the seal flap and then folding in one side at the crease to lay the end flap and the adjacent fourth side panel while still coplanar on top of the second and third side panels. Then the first panel is heated and folded in and its outer edge portion is pressed down on the heated seal flap with the outer edge lying directly on the fourth seam between the fourth panel and the seal flap. This forms a watertight seal between the seal flap and the first panel and creates the flat tube blank where the first and fourth panels lie atop the second and third panels, respectively.
Subsequently the tube blank is opened up to give it a rectangularly tubular shape, and one end of the opened-up blank is closed and the blank is stood on this closed end to form an upwardly open container or vessel. Then the contents are filled into the thus formed container and its upper end is closed.
In order to facilitate such subsequent handling of the flat tube blank it is standard practice to break in the creases, that is fold them back and forth so that they are not too stiff. This is typically done by holding the flat tube blank down on a conveyor belt with suction applied only to its third panel. Then the outer edges of the blank are pushed to one side until the second and first panels respective lie atop the third and fourth panels and the thus refolded blank is pressed between a pair of horizonal rollers to compress the second and fourth creases. Then the blank is bent back and is again passed through a pair of horizontal rollers to flatten the first and third creases. This moves all of the creases through 180.degree., effectively breaking them in so that the blank can subsequently be opened up and handled fairly easily.
This breaking-in is, however, a step which represents a substantial problem in the production of such boxes. The suction belt that holds down the tube blanks requires a high-capacity blower and makes a lot of noise, so that noise-suppressing shields and the like must be installed. The speed of the breaking-in equipment must be set according to the box length and the speed of the sealing machine so that the breaking-in equipment must have its own adjustable drive.